Some control systems of the prior art utilize separate microprocessors and bus drivers at the driver's door and at each of the right front, left rear, and right rear passenger positions, as well as a microprocessor under the dashboard. Usually only two common-bus conductors need be provided to each station. Both the microprocessors and the bus drivers for such systems are expensive and relatively bulky. The mean time between failure of the systems is greater because they have so many components.